Crankcase ventilator valve



OO I MANIFOLD DEPRESSION Dec- 20 1966 J. F. ARMSTRONG 3,292,656

cRANxcAsE VENTILATOR VALVE original Filed July 26, 1962 2 sheets-sheet z F IG.9. 54

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--\ .JAMES FRED ARMSTRONG AGENT United States NPatent O tion of New Jersey Continuation of application Ser. No. 212,515, July 26, 1962. This application Oct. 19, 1965, Ser. No. 505,581 11 Claims. (Cl. 137-480) This is a continuation of my co-pending application Serial No, 212,515, tiled July 26, 1962 andY now abandoned.

This invention is concerned with reduction of emission of atmospheric pollutants from automotive vehicles, and more particularly relates to a control for use in a system for Ventilating the crankcase of an internal combustion engine to the intake manifold of the engine for this purpose.

Tests recently conducted by the United States Public Health Service and the Southwest Research Institute have indicated that emission of gases containing unburned hydrocarbons from crankcases of automotive vehicle engines contributes substantially to smog in the atmosphere. These tests have indicated that from 20% to 35% of unburned hydrocarbons emitted by automotive vehicle engines come from the crankcase. The Los Angeles County Air Pollution Control District has estimated that 150 to 180 tons of unburned hydrocarbons are emitted daily from the crankcases of the engines of automotive vehicles in Los Angeles County. It will be understood that the presence of unburned hydrocarbons in the crankcase of the internal combustion engine of an automotive vehicle is due to what is called blow-by of gases past the pistons of the engine, i.e., leakage of gases past the pistons of the engine into the crankcase, and that ordinarily these blowby gases are vented from the crankcase into the atmosphere. Analysis of such blow-by gases has indicated that they comprise some 15% exhaust products and 85% carbureted mixture (i.e., a mixture of air and unburned fuel).

For the purpose of reducing pollution of the atmosphere by crankcase emissions (and also for the purpose of utilizing the unburned fuel otherwise wasted to the atmosphere), the crankcasemay be ventilated to the intake manifold of the engine for induction of crankcase fumes into the intake manifold. For proper operation of such a system without tinterference with normal performance of the engine, and for safe operation, the ow from the crankcase to the intake manifold must ybe properly metered and controlled, and provision must be made for prevention of backring from the intake manifold back into the crankcase.

Accordingly, among the several objects of this invention may be noted the provision of an improved control for such purposes, which is of such construction as to be economical to manufacture, comprising, for example, sheet metal parts which are economical to manufacture and easy to assemble; the provision of a control such as described which provides for effective metering of flow from the crankcase to the intake manifold in -accordance with the rate of blow-by (i.e., in general, the greater the rate of blow-by, the greater the rate of induction of fumes from the crankcase into the intake manifold), and which is so constructed as to avoid becoming clogged by dirt, carbon, or sludge (such as may result from emulsication of oil from the crankcase and water), being in effect selfcleaning, and thereby reliably providing for effective metering; the provision of a control such as described adapted to take care of blow-by at the maximum rate at which blow-by may occur (as at wide-open throttle) but without excessive leaning of the air/fuel mixture supplied to the engine via the intake manifold under other 3,292,656 Patented Dec. 20, 1966 "ice conditions to avoid poor engine performance or stalling; and the provision of a control such as described adapted automatically to prevent backfiring through the control without interfering with proper ow through the control to the intake manifold under normal conditions. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIGURE 1 is a transverse vertical section of an internal combustion engine having a system for Ventilating the crankcase of the engine to the intake manifold of the engine including a control of this invention;

FIGURE 2 is -a longitudinal section of the control per se, showing a movable valve member thereof in a socalled idle position;

FIGURE 3 is a bottom plan of FIGURE 2, with certain parts broken away and shown in section;

FIGURE 4 is a view corresponding to FIGURE 3 showing the movable valve member in an intermediate position;

FIGURE 5 is a view corresponding to FIGURE 3 showing the movable valve 4member in a so-called backfire position;

FIGURE 6 is a section of an alternative form of control of this invention, showing the movable valve member thereof in idle position;

FIGURE 7 is a view corresponding to FIGURE 6 showing the movable valve member thereof in an intermediate position;

FIGURE 8 is a view corresponding to FIGURE 6- showing the movable valve member thereof in backfire position;

FIGURE 9 is a detail of a valve seat used in the FIGf URE 6 control; and

FIGURE l0 is a graph showing how flow through a control of this invention varies in relation to variation in intake manifold vacuum, the ow being plotted in terms of cubic feet per minute and the intake manifold vacuum being plotted in terms of manifold depression in inches of mercury, and also showing the relationship of variation in flow to the variation in the rate of blow-by.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawlngs.

Referring to the drawings, there is indicated at 1 in FIGURE 1 an internal combustion engine, shown as a V-8 engine comprising a cylinder block 3 having two banks of four cylinders each. One of these cylinders is shown in section in FIGURE 1, and designated 5. On each bank of cylinders is a cylinder head 7 having valve seats such as indicated at 9 for the valves such as indicated at 11 which control flow of air/fuel mixture from intake manifold 13 of the engine through passages such as indicated at 15 to the cylinders. On the intake manifold is the carburetor 17 for supplying air/fuel mixture to the intake manifold and including a throttle (or throttles) for controlling the flow of air `and fuel -to the intake manifold. The crankshaft of the engine is indicated at 19, and the crankcase at 21. The pistons of the engine are indicated at 23, and the connecting rods which connect the pistons and lthe crankshaft are indicated at 25. It will be understood that when fuel is burned in a cylinder 5, gases tend to blow by the respective piston 23 into the crankcase, particularly `after Wear has occurred, these gases including unburned fuel as above pointed out.

On each cylinder head 7 -there is a cover for the valve operating mechanism indicated at 27. One cover is designated 29a, the other 29h. An oil filler pipe 31 is shown as extending from cover 29a with la breather cap 33 on the pipe. This cap is of such nature `as to permit entry of air to pipe 31 as indicated by Athe arrows in FIGURE 1. Passages such as indicated at 35 are provided for flow of oil poured into the filler pipe into the crankcase. These also provide for fiow of air from the pipe into the crankcase. The cylinder block 3 and the cylinder head associated with the other bank of cylinders have passages such as indica-ted at 37 for flow of air and blow-by gases from the crankcase into cover 29b. The latter has an outlet at 39 connected by a conduit 41 to the inlet of a control C of this invention, the outlet of the control C being connected by a conduit 43 to the intake manifold for induction of crankcase fumes into the intake manifold.

Now referring to FIGURES 2-5,'control C is shown to comprise 'a two-piece valve body or'h-ousing designated in its entirety by reference character 51, and comprising a first cup-shaped housing member 53 formed with an axial linlet nipple 55 for connection of conduit 41, and a second cup-shaped housing member 57 provided with an axial outlet nipple 59. Housing member 53 is telescoped in housing member 57, and these parts are secured together in suitable manner to provide a sealed cylindric chamber 61 with an inlet 55 and an outlet 59. Housing members 53 and 57 may economically be made of sheet metal, for example, and brazed together at 63. Nipple 55, as shown in FIGURES 2, 4 and 5, is an integral part of member 53 1' extending axially from the end wall 65 of member 53. Nipple 59, as shown in FIGURES 2, 4 and 5, is a separate tubularpart (and may be a sheet metal part) extending through a central hole 67 in end wall 69 of member 57 and press-fitted in a fixed tubular sleeve valve member 71 extending axially in cylindric chamber 61 from end wall 69 and terminating well short of end wall 65 of housing member 53. Nipple 59 has an annular bead 72 engaging the outside of end wall 69 around hole 67, and the outlet end of tubular sleeve Valve member 71 engages the inside of end Wall 69 around hole 67.

The fixed tubular sleeve valve member 71 projects beyond the inner portion of nipple 59 and, adjacent its free inner end, has a pair of axially spaced external annular ribs 73 and 75. A cup-shaped movable valve sleeve member 77 is telescoped on member 71 over its free end and is axially slidable on ribs 73vand 75 of member 71. The cylindric wall of member 77 is designated 79 and its end wall is designated 81. Each of members 71 and 77 is of thin-walled construction, and may economically be sheet metal parts (stainless steel, for example). The cup-shaped valve member 77 has a central orifice 83 in its end Wall 81. This orifice, as will appear, constitutes an idle port. The movable valve member 77 :also has a main port 85 in its cylindric wall 79 adjacent its end wall 81. The cup-shaped valve member 77 is slidable on the xed valve member 71 between the idle position in which it is shown in FIGURE 2, wherein it is fully retracted relative to member 71, and the backfire position in which it is shown in FIGURE 5, wherein it is extended relative to member 71. The backfire position is determined by engagement of the periphery of end wall 81 of the cupshaped member 77 with the end wall 65 of housing member 63 around the inlet 55, the end Wall 65 serving as a valve seat in conjunction with the periphery of wall 81 to block flow from the space in chamber 61 around member 77Ato the inlet. The idle position is determined by engagement of the inside of end wall 81 with the free end of member 71. In the idle position of member 77, main port 85 is located between ribs 73 and 75 .and thereby blocked. As member 77 slides to the left from idle position as viewed in FIGURE 2, port 85 crosses rib 73 and opens up to the interior of member 77. As vappears in FIGURE 3, port 85 is of T-shape with the stern of Ithe T extending longitudinally of member 77, and the head of the T at the right end of the stem of the T.

differential.

The cylindric wall 79 of movable valve member 77 has struck-out ears 87, Aand a coil compression spring-89 surrounds member 77 between these ears and end wall 69 of housing member 57, reacting from wall 6'9 to bias member 77 to slide toward the left away from idle position. FIGURE 5 shows the spring in its state of maximum extension. Its length at maximumrextension plus the distance measured along member 77 from the right-hand faces of the ears to the left end of member 77 is somewhat less than the length of chamber 61. Accordingly, spring 89 biases member 77 only to a position somewhat short of its FIGURE 5 backfire position, and further movement of member 77 toward backfire position is away from the end of the spring. The interval of such springbias-free movement of member 77 is indicated at A in FIGURE 5.

With the inlet 55 of control C connected to the crankc-ase and the outlet 59 of control C connected to the intake manifold of the engine 1 as appears in FIGURE 1, the cup-shaped valve member 77 of control C is subject to the difference in pressure inthe crankcase and in the intake manifold on opposite sides of its end wall 81. When thte engine is operating with the throttle or throttles of carburetor 17 closed or substantially closed, a relatively high vacuum is drawn in the intake manifold. Such a condition occurs during engine idling or when the engine is braking the speed of the vehicle, with the -throttles closed at any speed. Accordingly, Ithere is a relatively low pressure in outlet 59 and hence a relatively high pressure differential tending to move the valve member stricted flow from the inlet 55 through the restricted` orifice or port 83 in the end wall 81 of member 77. This is suicient to take care of the relatively low rate of blow-by under closed throttle conditions.

Upon opening the throttle or throttles of carburetor 17 to speed up the engine from idle, the vacuum in the intake manifold decreases. Thus, pressure in outlet 59 increases and the pressure differential on end wall v81 of member 77 decreases. When the pressure differenti-al becomes less than the bias of spring 89,-the spring moves valve member 77 to the left as viewed in FIGURE 2 away from its -idle position. As the member 77 slides to the left, the left end ofthe stem portion of the T-shaped port pass the rib 73, .and communication is lished from inlet 55 to outlet 59 via port 85 and the interior of fixed tubular valve member 71 Yfor the inlet to the outlet via port A85 in addition to idle port 83. As port 85 is increasingly opened spring 89, the air flow through port 85 increases since the area of the opening of port 85 is chosen to more than compensate yfor the corresponding decrease in pressure The flow of air through valve C becomes a maximum when port 85 completely passes rib 73and is fully opened. This would occur as the throttle of the carburetor is opened for high speed or under load operating conditions of the engine, when iblow-by is at a maximum. Upon closing the throttle or throttles of the carburetor, vacuum in .the intake manifold increases, meaning that pressure in outlet 59 decreases, and valve member 77 moves toward the right, port 85 closing off as it slides past rib 73.

Thus, in response to liuctuation in vacuum in the intake manifold, as reflected in liuctuation of pressure in outlet 59, valve member 77 moves in one direction or the other to vary the rate of liow through the control C. Preferably, the calibration of the control (including the selection 'of the spring 89 and the size `and shape of port 85) is such as to effect increase and decrease in the thereby estabflow from t under action of rate of flow through the control in substantially direct proportion to the increase and `decrease in the rate of blow-by. As the rate of blowby is generally an inverse function of intake manifold vacuum, i.e., the higher the intake manifold vacuum, the lower the rate of blow-by, and vice versa. This is illustrated in FIGURE 10, where line A is a typical characteristic blowaby curve, illustrating .the `decrease in rate of blowdby as the vacuum in the intake manifold increases (i.e., as the pressure in the intake manifold decreases). Line yB illustrates the manner in which the rate of ow through control C varies with variations in the intake manifold vacuum. As will apmar from FIGURE I10, line B 4generally parallels line A in a range of manifold vacuum values between 2-4 inches of mercury at one end to Il4-l-8 inches at the other end. The valve 51 is wide open from zero manifold depression to a value represented by the peak of curve B around 2 to 4 inches of mercury of manifold vacuum. This portion of curve B also represents the operation of the engine at wide open throttle. The T-shape shown for port 85 is only exemplary of various suitable `shapes that may be used. High manifold vacuum is also present in the engine .at speeds Iother than idle when the throttle is closed and the engine is braking the speed of the vehicle at any speed. Thus the right-hand portion of curve B in FIGURE l0 represents braking and idling operation of the engine.

It is to be noted that spring 89 biases valve member 77 only partially tow-ard the FIGURE 5 backfire position. This means that `spring 89 is ineffective to seat end wall 81 of member 77 against end wall 65 of housing part 53 even with low vacuum (i.e. pressure approaching atmospheric pressure) in outlet 59, `as occurs under wide-open throttle conditions. This assures flow through control C via port 85 at wide-open throttle, t-o take care of blowby `under such'conditions.

I-n the event of backfiring in the intake manifold, the resultant high pressure :in the outlet 59 rapidly drives valve member 77 to its FIGURE 5 backtire position wherein the periphery of its end wall 81 engages the end wall `65 of housing part 53 laround the inlet 55. This blocks the outlet from the inlet, except for the idle port 83, and prevents .backring into the crankcase. This is important to avoid danger of explosion or tire in the crankcase. Idle port 83, being a port of restricted size, is small enough to prevent propagation of llame back into the crank-case, while being ladequate `for proper .flow from the inlet to the outlet under engine idling conditions.

lt is to be especially noted that valve members 71 and 77 are in the nature of sleeve valve members, of thin-walled construction. This is important in avoiding such clogging of the control by dirt, carbon, sludge or the like as 4would upset the metering function of the control. With member 77 sliding on rib 73 of member 71, there is a tendency for the control to be selfacleaning as regards port 85, and with idle port 83 being in the thin end wall 81 of member 77, it is of very short length, Iand much less likely to become clogged than a relatively longV port.

FIGURES 6-8 illustrate a modi-fied control C1 with a lateral inlet, and with complete cut-off on backre. Control C1 comprises a two-piece valve body or housing 51a, comprising cupshaped parts 53a and 57a secured together as appears in FIGURES `6--7 to provide chamber 61. Part 57a has a lateral inlet nipple 55a and, the same axial outlet nipple 59 as control C. As in control C, tubular sleeve valve member 71 extends linward ffrom the inner end of nipple 59 and has the ribs 73 and 75. Cup-shaped sleeve valve member 77 is slidable on member 71 the rsame as in cont-rol C. Spring 89 acts against a collar 91 on member 77, and this collar is adapted to seat against an annular valve seat 93 for cut-off on backfire. This seat 93 is clamped between the rim of the cup-shaped housing part 57a and an annular shoulder 95 formed on housing part 53A. The cup-shaped member 477 slides in the central opening 97 in seat 93, this opening having radial recesses as indicated at 99 for flow therethrough around member 77.

With valve member 77 of control C1 in its FIGURE 6 high mani-fold vacuum position, restricted air liow ocours from linlet l55a through recesses 99 and port 83 to the outlet 59, when the throttle is closed during engine idling or braking operation. With valve member 77 of control C1 in its FIGURE 7 open-throttle position, flow occurs from inlet 55a through recesses 99 .and port 85, as well as through idle port 83. In the event of :a backfire, valve member 77 is driven to its FIGURE 8 backfire wherein collar 91 engagesl seat 93 completely to block the outlet 59 lfrotm the inlet 55a.V As in control C, spring 89 in control C1 biases valve member 77 -only partially toward the FIGURE 8 backfire position, the internal of spring-bias-free movement of member 77 being indicated at A in FIGURE 8.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be. made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. For example, the size and shape of the ports and 83 are selected to conform with the engine, with which the valve is to be used and for optimum engine operation at all speeds. The stiffness of spring 89 is also selected to provide the desired cut off of air ow under high manifold vacuum. This could be at any desired negative pressure above an optional value such as 14 inches of Hg.

I claim:

1. A crankcase ventilator valve comprising a body dening a chamber and having an inlet for connection to the crankcase of an engine and an outlet for connection to the intake manifold thereof, a tubular sleeve valve member fixed in relation to said body within said chamber in communication at one end with said outlet and having its other end free, a cup-shaped sleeve valve member telescoped on said fixed valve member over its free end and slidable back and forth on said fixed valve member between an idle position closing the outlet and a backre position closing the inlet in which it prevents backflow therethrough and having a range of intermediate positions, and means biasing said slidable valve member to slide in the direction away from idle position, said biasing means being constructed and arranged to effect only partial movement of the said slidable valve member toward the backfire position, the valve member moving to a full backiire position relative to the biasing means upon an increase in pressure in the outlet for preventing backow into a crankcase,said slidable valve member being slidable in the direction toward idle position against the bias in response to decrease in pressure in the outlet to close the outlet and slidable in the direction toward backre position in response to a predetermined increase in pressure in the outlet to close the inlet, said slidable valve member having a port therein for establishing communication from the inlet to the outlet in said intermediate positions of said slidable valve member, said port being blocked by said fixed valve member when said slidable valve member is in idle position.

2; A valve as set forth in claim 1 wherein said cupshaped slidable valve member has an idle port therein for restricted communication from the inlet to the outlet when said slidable valve member is in idle position.

3. A valve as set forth in claim 1 wherein said port is shaped to act on sliding of said slidable valve member in said range to increase and decrease the rate of flow from the inlet to the outlet in substantially direct proportion to the increase and decrease in the rate of ilow of the inlet.

g 4. A valve-as set forth in claim 3 wherein said cupshaped slidable valve member has an idle port therein for restricted communication from the inlet to the outlet when said slidable valve member is in idle position. Y

5. A cranlrcaser ventilator valve comprising a body formed of two cup-shaped sheet metal parts secured together and defining a chamber, said body having an inlet for connection to the crankcase of an engine and an outlet for connection to the intake manifold thereof, a tubular sheet metal sleeve valve member fixed in rela'- tion to said body within said chamber in communication at one end with said outlet and having its other end free, a cup-shaped sheet metal sleeve valve member telescoped lon said fixed valve member over its free end and slidable on said fixed valve member between a retracted position relative to said fixed valve member and an extended position relative to said fixed valve member and having a range of intermediate positions, said retracted position constituting an idle position and said extended position constituting a backfire position in which said cup-shaped valve member prevents backfiow therethrough, a spring biasing said cup-shaped valve member to slide in the direction away from idle position and said cup-shaped Nvalve member being slidable in the direction toward idle vposition against the bias of said spring in response to decrease of pressure in the outlet, said spring having a free length such as to effect only partial movement of said cup-shaped valve member to its backfire position,

said cup-shaped valve member being movable to the full backfire position upon a predetermined increase in pressure at the said outlet, said cup-shaped valve member having a main port in the cylindric wall thereof for establishing communication from the said inlet to the said outlet in said intermediate positions of saidvcup-shaped valve member, said main port being blocked by said fixed valve member when said cup-shaped valve member is in` idle position, and said cup-shaped valve member having an idle port in the end wall thereof for restricted communication from the inlet to the outlet when said cup-shaped valve member is in idle position.

6. A valve as set forth in claim 5, wherein said fixed valve member has a pair of axially spaced external annular ribs on which said cup-shaped valve member is slidable, said main port being located between said ribs when said cup-shaped valve member is in idle position.

7. A valve as set forth in claim 6, wherein said main port is shaped to act on sliding of said cup-shaped valve member in said range to increase and decrease the rate of iiow from the inlet to the outlet in substantially direct proportion to the increase and decrease in the rate of ow at the inlet.

8. A valve as set forth in claim 7, wherein said inlet and said outlet are substantially coaxial at opposite` ends of said body and the end wall of said cup-shaped valve member, when in backfire position, engages the inlet end of said body around the inlet.

9. A valve as set worth rounding said cup-shaped valve member engageable by said collar upon movement of said cup-shaped valve` member to backfire position.

10. A crankcase ventilator valve comprising a body defining a chamber and having an inlet for connection to the crankcase of an engine and an outlet for connection to the intake manifold thereof, a iiow control valve mem` ber in said body movable between an idle position clos-l ing the outlet and a backfire position closing the inlet -and having a range of intermediate positions for metering flow in accordance with engine requirements, spring biasing means for biasing said valve member to move'ina direction away from idle position, said biasing means being constructed and arranged to effect only partial movement of the said valve member toward the backfire position, the valve member moving to a full backfire position relative to the biasing means in response to a predetermined increase in pressure in the said outlet to close the said inlet and said Valve member being movable in the direction toward idle position against the bias of the said spring in response to a decrease in pressure in the outlet.

11. A crankcase ventilator valve comprising a body idle position, said valve member being movable in the` direction toward idle position against the bias of said spring in response to decrease of pressure in the said outlet, said kspring having a free length such as to effect only partial movement of said valve member to its backfire position, said valve member being movable to the full backfire position upon a predetermined increase in pressure at the said outlet.

References Cited by the Examiner UNITED STATES PATENTS 2,584,418 2/195-2 Branson 137-504 2,716,398 8/1955 McMullen 123-119 2,938,538 5/1960 Allen 137-504 3,111,138 11/1963 Humphreys 137-480 WILLIAM F. ODEA, Primary Examiner.

HAROLD WEAKLEY, Examiner.

in claim 7, wherein the inlet` is a lateral inlet and the outlet is an end outlet, said cup` shaped valve member has a collar engaged by the sprin'g, and said body has an annular valve seat therein sur-1 

1. A CRANKCASE VENTILATOR VALVE COMPRISING A BODY DEFINING A CHAMBER AND HAVING AN INLET FOR CONNECTION TO THE CRANKCASE OF AN ENGINE AND AN OUTLET FOR CONNECTION TO THE INTAKE MANIFOLD THEREOF, A TUBULAR SLEEVE VALVE MEMBER FIXED IN RELATION TO SAID BODY WITHIN SAID CHAMBER IN COMMUNICATION AT ONE END WITH SAID OUTLET AND HAVING ITS OTHER END FREE, A CUP-SHAPED SLEEVE VALVE MEMBER TELESCOPED ON SAID FIXED VALVE MEMBER OVER ITS FREE END AND SLIDABLE BACK AND FORTH ON SAID FIXED VALVE MEMBER BETWEEN AN IDLE POSITION CLOSING THE OUTLET AND A BACKFIRE POSITION CLOSING THE INLET IN WHICH IT PREVENTS BACKFLOW THERETHROUGH AND HAVING A RANGE OF INTERMEDIATE POSITIONS, AND MEANS BIASING SAID SLIDABLE VALVE MEMBER TO SLIDE IN THE DIRECTION AWAY FROM IDLE POSITION, SAID BIASING MEANS BEING CONSTRUCTED AND ARRANGED TO EFFECT ONLY PARTIAL MOVEMENT OF THE SAID SLIDABLE VALVE MEMBER TOWARD THE BACKFIRE POSITION, THE VALVE MEMBER MOVING TO A FULL BACK FIRE POSITION RELATIVE TO THE BIASING MEANS UPON AN INCREASE IN PRESSURE IN THE OUTLET FOR PREVENTING BACKFLOW INTO A CRANKCASE, SAID SLIDABLE VALVE MEMBER BEING SLIDABLE IN THE DIRECTION TOWARD IDLE POSITION AGAINST THE BIAS IN RESPONSE TO DECREASE IN PRESSURE IN THE OUTLET TO CLOSE THE OUTLET AND SLIDABLE IN THE DIRECTION TOWARD BACKFIRE POSITION IN RESPONSE TO A PREDETERMINED INCREASE IN PRESSURE IN THE OUTLET TO CLOSE THE INLET, SAID SLIDABLE VALVE MEMBER HAVING A PORT THEREIN FOR ESTABLISHING COMMUNICATION FROM THE INLET TO THE OUTLET IN SAID INTERMEDIATE POSITIONS OF SAID SLIDABLE VALVE MEMBER, SAID PORT BEING BLOCKED BY SAID FIXED VALVE MEMBER WHEN SAID SLIDABLE VALVE MEMBER IS IN IDLE POSITON. 